In a semiconductor device manufacturing process, in order to separate a capacitor or a device or to form a contact hole, a dry etching is performed on a substrate, e.g., a semiconductor wafer (hereinafter, referred to as “wafer”), on which a resist mask is formed, and, then, an ashing process is carried out to remove the resist remaining on the surface after the etching process. As one of methods for performing such processes, there has been known a plasma processing method employed in a single sheet parallel plate type plasma processing apparatus.
Hereinafter, a schematic constitution of such plasma processing apparatus will be briefly described with reference to FIG. 6. In such a plasma processing apparatus, an upper electrode 11 serving as a gas shower head and a mounting table 12 serving as a lower electrode and also as a cooling plate are installed at an upper and a lower portion in a processing chamber 10 having a vacuum exhaust unit 10, respectively, and a high frequency power supply 13 for forming a high frequency electric field between the electrodes is connected to the upper electrode 11. Further, a wafer mounting region on an electrostatic chuck 14 installed on top of the mounting table 12 is formed smaller than a size of a wafer W. A ring member 15, e.g., a quartz ring, is installed so as to surround an entire circumference of the electrostatic chuck 14. The ring member 15 is disposed to face a side peripheral surface and a bottom peripheral portion of the wafer W protruded outwardly from the mounting region with a gap formed therebetween. Moreover, formed on a surface of the electrostatic chuck 14 are gas supply openings (not shown) for supplying a thermally conductive He gas to be outwardly diffused from a central portion through gaps formed by slight irregularities on surfaces of the wafer W and the electrostatic chuck 14.
Mounted on the mounting table 12 is the wafer W on which an insulating film made of, e.g., SiO2 and a resist mask of a circuit pattern are laminated. Further, a chuck voltage is applied to the electrostatic chuck 14 and an inner space of the processing chamber 1 is vacuum-exhausted by a vacuum exhaust unit 10. In such state, an etching gas containing a compound of C and F (e.g., CxFy) is plasmarized, thereby etching the insulating film. Next, a supply of the etching gas is stopped and an ashing gas containing O2 is then supplied into the processing chamber 1. The ashing gas is plasmarized by forming a high frequency electric field, so that the resist exposed to the plasma is ashed and removed. Accordingly, after having undergone such processes, the insulating film on the wafer W has therein grooves corresponding to the circuit pattern.
However, if the etching process is performed by using a plasma of a CF-based gas, as schematically illustrated in FIG. 7, a polymer mainly composed of CFx, which is generated by a decomposition or a reaction of the etching gas, is adhered to the bottom peripheral portion and the side edge surface of the wafer W. In other words, the mounting table 12 is formed in a smaller size than the wafer W to prevent damages inflicted by the etching gas. Further, in general, the ring member 15, referred to as, e.g., a focus ring, for adjusting a plasma shape is installed so as to surround the wafer W. In order to prevent the gas from flowing toward the bottom surface of the wafer W, a stepped portion 15a is formed at an inner side of the ring member 15 such that it extends into a space under the bottom surface of the wafer W. However, it is not sufficient to prevent the plasma from flowing into the space, so that deposits of the polymer are adhered to the bottom peripheral portion of the wafer W.
In the ashing process after the etching process, the plasma of the ashing gas containing O2 flows into the aforementioned space along a slight gap between the peripheral portion of the wafer W and the ring member 15. Accordingly, the deposits adhered to the bottom peripheral portion and the side edge portion of the wafer W become ashed. However, a considerable time period is required to completely remove the deposits and, in some cases, the deposits are not completely removed.
Meanwhile, if the deposits are adhered to the bottom peripheral portion (and the side edge portion) of the wafer W, they are separated therefrom in a post-process to be a cause of particles. Further, in a chemical polishing process as the post-process, portions to which the deposits are adhered are stressed, thereby deteriorating polishing accuracy. Accordingly, the wafer W that has gone through the ashing process is subjected to a cleaning process using cleaning fluid in a cleaning vessel. In this case, the deposits detached from the wafer W may be introduced into the cleaning vessel and transcribed on another wafer, so that an exchange cycle of the cleaning fluid in the cleaning vessel needs to be frequently performed. In order to sufficiently remove the deposits during the ashing process after the etching process, it is considered to extend the ashing time to allow the plasma to reach the bottom peripheral portion of the wafer W. In this case, however, depending on types of the insulating film, the film may be changed in quality.
As for an interlayer insulating film, for example, a SiOC film, i.e., a compound of silicon, oxygen and carbon, is widely used due to its low dielectric constant. However, if the film is exposed to an oxygen plasma for a long time, a surface thereof becomes oxidized, thereby changing SiOC to SiO2. The SiO2 is removed in a post-cleaning process, resulting in a wider line width. Further, the increase in the ashing time deteriorates a throughput thereof.
A conventional sequence of the plasma processing includes the steps of: stopping a supply of a thermally conductive gas after a specific processing is performed by using a plasma; stopping an application of a chuck voltage to the electrostatic chuck; and stopping a supply of a power for generating the plasma (see, e.g., Japanese Patent Laid-open Publication Nos. H4-290225 and H8-153713). However, there is not disclosed nor suggested any process after the processing described above.